Thermal cutout switch



April 15, 1952 Filed Feb. 1, 1949 E. A. HAVASI THERMAL CUTOUT SWITCH 2 Sl-IEETS-SHEET l BIMETALLIC MATER|AL 2 l6 r i i I l I l\ 1 I0 I? mm s 4 9 INPUT RECTIFIER FlG.

TRANSFORM-ER JSI Q JNVENTOR. )6 I BY I 14; 1%.: V54 4x 4 April 15, 1952 E. A. HAVASI THERMAL CUTOUT SWITCH Filed Feb. 1, 1949 FIG. 3

BIMETALLI'C MATERIAL FIG. 4

IN VEN TOR.

BIMETALLIC MATERIAL Patented Apr. 15, 1952 THERMAL CUTOUT SWITCH Emil Arthur Havasi, Cuba, N. Y., assignor to Acme Electric Corporation, a corporation of New York Application February 1, 1949, Serial No. 73,990

2 Claims. 1

My invention relates to a thermal cut-out switch which will automatically break the circuit upon occurrence of abnormal current conditions.

In describing my invention I will refer to the specific use of the thermal cut-out switch to disengage or cut-out the circuit of a battery charger, when the connections of the charger are reversed. The switch is connected in series with a. low voltage rectifier, the secondary winding of the transformer and the battery. These thermal cut-out switches are primarily designed to cut out at a predetermined current and when the connections of the battery charger are reversed to prevent damage to the rectifier and the trans former.

Thermal cut-out switches have been used in battery chargers and other electrical equipment to break the circuit when an overload or eXcessive current is present. In these thermal cut= out switches, the contact is generally made by depressing a bi-metal arm against a stationary switch contact. Since the bi-metal arm is connected in series with the circuit, the current flows through the arm and heats it. Many times the operators burn the contact points between the arm and the stationary contact by not engaging the contacts properly. When the contacts are not engaged properly, an arc is drawn between the tip of the arm and the stationary contact. This are either gradually burns the end of the bi-metal switch arm thus destroying the switch or tends to weld the arm to the contact. Very often the operators would place their fingers on the bi-metal arm to depress it and engage it with the stationary switch contact before the arm had cooled thus resulting in the burning of the operators fingers.

I have developed a new thermal cut-out switch which overcomes these problems and which pr vent-s damage to the bi-metal switch and burning of the operators fingers. One of the objects in developing my new thermal cut-out switch is to provide a cut-out switch in which the contacts between the bi-metallic arm and the stationary contact can not draw an arc.

Another object of my invention is to provide a thermal cut-out switch which may be reset Without possibility of the operator burning his fingers.

Another object of my invention is to provide a temperature responsive switch and a manually operable switch connected in series with the manually operable switch breaking circuit and engaging the bi-metal arm of the temperature responsive switch to move it into engagement with its respective contact or terminal.

Another object of my invention is to provide a thermal cut-out switch which is safe to operate and which is economical to manufacture.

Another object of my invention is to provide a thermal cut-out switch comprising. spaced thermals with a bi-metal arm and a spring arm electrically connected together and disposed between these terminals with the spring arm positioned in engageable alignment with the bi-metal arm to move the bi-metal arm into latching engagement with one of the terminals.

Another object of my invention is to provide a thermal cut-out switch in which the switch cannot be reset without opening the circuit in which the switch is connected.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

Figure 1 of drawings illustrates a side view of my thermal cut-out switch with the switch diagrammatically electrically connected in the battery charger circuit.

Figure 2 illustrates a top view of the thermal cut-out switch;

Figure 3 illustrates a bottom View of the thermal cut-out switch;

Figure 4 is a side View of Figure 1 showing the position of the switch arm immediately after the switch has broken an overload circuit; and, Figure 5 illustrates the side view of Figure 1 with the spring arm depressed and engaging the bi-metal arm to latch it over the latch terminal.

Referring to the drawings the reference character Iii represents an insulation support to which the component parts of my thermal cutout switch are fastened. This insulation sup port iii carries a latch terminal II and a latch arm H! which is aligned for latching engagement with the latch terminal I I. The insulation support It] also carries an abuttable terminal l3 and a spring contact arm 14 normally abutting this terminal. The abuttable terminal I3 is spaced from the latch terminal H and the spring contact arm 24- and the latch arm I2 are disposed therebetween with the spring arm I4 electrically connected to the latch arm 12 and pcsitioned'in engageable alignment therewith.

The insulation support I0 is described as having a top surface [5 and a bottom surface [1. The insulation support may be fastened in the housing of the battery charger by bolts or other suitable meam which may extend through openings it. The latch terminal II is disposed on the bottom surface I! of the insulation support 10 and terminates in a latch edge 20. The insulation support I has an opening I9 therein and across which this latch edge 20 of the latch terminal II extends. I have illustrated the latch terminal I I as having ears 2I on the sides thereof with these ears 2| extending upwardly through the insulation support Ill and engaging the top surface I6 thereof to securely hold the latch terminal I I onto the insulation support III.

The latch arm I2 is preferably constructed from a bi-metal member having a free end pore tion 24 extendable through the opening I 9 and also having a fastening end 25. The bi-metal latch arm I2 is fastened at the fastening end 25 thereof to the top surface It of the insulation support I0 and at a distance from the opening I9. The bi-metal arm has spring-like properties urging the free end 24 through the opening I9. away from the latch terminal II. The free end portion 24 is disposed at an angle to the remainder of the latch arm and integrally con.- nected thereto by a curved bi-metal portion 25.

The fastening end portion 25 of the latch arm I2 may. be fastened to the top surface lb of the insulation support Iii by rivets or other suitable means. However, I have found it advisable to use a fastening member 2"! having fastening portions 28 extending through the insulation sup port II] and engaging the fastening end portion 25. The fastening member 27 is disposed against the bottom surface II and these fastening portions 28 clamp the fastening end portion 25 of the latch arm I2 tightly against the top surface I6 of the insulation support.

When the lei-metal arm or latch arm I2 is maintained below a predetermined temperature, the free end portion 24 which extends below the opening I9 in the insulation support Ill may be latched over the latch edge 28 of the latch terminal II. Should an overload condition exis the contour of the bi-metal at the curved bi -metal portion 26 will tend to flatten this curved portion in response to the over heating of this arm by the current passing therethrough. The flattening of the curved bi-metal portion 28 results in disengagement of the free end portion 24 with the latch edge 20. The spring like properties of the latch arm I2 snap the free end portion 24 through the opening I9 away from the latch terminal I I.

The abuttable terminal I3 is preferably constructed from a stamping and is preferably fastened to the insulation support It by a rivet 3b. This abuttable terminal I3 has an abutment contact portion 3% disposed at a distance from the top surface Iii. The abut-table terminal I3 also has a wire connection portion 32 extending from the top surface I past the bottom surface I? and outwardly away from the insulation support III to provide means for connecting a wire to the abuttable terminal.

The spring contact arm I i comprises in general a fastening portion 34 and an extended arm portion 35. In my drawings I have illustrated the fastening portion 34 and the arm portion 35 as extending at an angle to each other with the fastening portion 3d riveted to the top surface of the insulation support by means of a rivet 36. The fastening portion 38 has a part thereof extending through an opening 3? in the insulation support It for electrical connection to the fastening member 21, which fastens the latch arm I2 to the insulation support. A wire 38 or any other suitable electrical connection means may be used to electrically connect the fastening portion 34 and the fastening member 27 thus electrically connecting the spring contact arm I4 and the latch arm I2 in series.

The extended arm portion 35 of the spring contact arm I4 is disposed in engageable alignment with the bi-metal or latch arm I2 and between the latch terminal I I and the abuttable terminal I3. The spring like properties of the spring arm I4 urge the arm against the abutment contact portion 3! of the abuttable terminal I3. When the spring arm I4 is moved away from the abuttable terminal I3 and towards the latch terminal II, the electrical contact is broken between the manually operable spring member I4 and the abuttable member I3. As the abuttable spring member isfurther moved towards the latch terminal II it engages the latch arm I2 and moves the free end portion 24 thereof against the latch edge at and into the latch engagement with the latch terminal I I.

"InFigure 1 of my drawings I illustrate the latch terminal II, the latch arm I2, the spring contact arm I l, and the abuttable terminal I3 as being electrically connected in series in the output side of a battery charger. The latch terminal II and the bi-"netal latch arm I2 may be considered a temperature responsive switch and the abuttable terminal I3 and the spring arm I4 may be considered a manually operable switch connected in series therewith. As long as the charger is operating correctly the current flowing through the switches and through the bi-metal arm I2 will not be sufficient to heat the curved portion 26 of the bi-metal arm above a predetermined temperature. However, should the cur rent flowing through the switches become excessive due to an overloading of the charger or to incorrectly connecting the output of the battery charger to a battery the curved portion 26 will flatten and the spring properties of the latch arm I2 will snap the free end portion 24 away from the latch edge 20 of the latch terminal II.

In Figure 4 I best illustrate the position of the component parts of the switch immediately after an overload. In this figure the free end portion 24 is shown disconnected or disengaged from the latch terminal II, thus breaking the circuit and preventing damage to the rectifier and transformer in the battery charger. Figure 4 also i1- lustrates that the spring-like properties of the spring contact arm I4 hold the spring contact arm I l against the abuttable terminal I5. When the temperature responsive switch is reset to again close the circuit the operator simply moves the spring contact arm III away from the abuttable terminal I3 and against the latch arm I2 to move the free end portion 24 into engagement with the latch terminal I I.

Many times the operators will attempt to close the switch before the overload condition has been corrected. Attempting to close this switch before the overload condition has been corrected causes an excessive sparking between the free end portion 24 and the edge 26. This excessive sparking either welds the free end portion 24 of the bi-metal arm to the terminal II or burns-the end off so that it will not latch over the latch edge 23. I have discovered that on closing the circuit before the overload condition has been corrected often results in currents of amperes flowing through the bi-metal latch arm I2 and the terminal I I. In normal operation the switch is constructed to carry approximately 8 amperes before it reaches the predetermined temperature which causes it to break the circuit. A switch constructed to withstand 8 amperes of current normally will not last long when 60 amperes are put through the contact points.

I have also discovered that the interval of time required to reset the switch and latch the end portion 24 over the latch edge 26 is relatively long. During this time a continual expansion and contraction of the bi-metal arm occurs. There are a series of repeated makes and breaks in the electrical circuit between the free end portion 24 of the bi-metal arm I2 and the latch II during this resetting time. It is well known that the response of the bi-metal spring properties under these repeated make and break conditions decreases until substantially all the elasticity is finally destroyed by the excessive heat generated by the bi-metal arm. Thus, the bi-metal arm I2 will eventually alter into a piece of material which would be easily welded to the edge 20 of the latch terminal II.

' In my cut-out switch the electrical circuit is broken between the abuttable terminal I3 and the latch terminal II as is illustrated in Figure 5 while the latch arm I2 is engaged with the latch terminal II. By breaking the circuit between the abuttable terminal I3 and the spring contact arm II excessive currents which would cause welding or burning of the delicate and sensitive temperature responsive switch are prevented. No current can flow again through the circuit until the pressure used to urge the spring contact arm I4 into the engagement with the latch arm I2 and away from the abuttable terminal I3 is released. As soon as this pressureis released the spring properties of the contact arm 54 will cause it to snap against and thereby abutt against the abuttable terminal I3 thus completing the circuit.

In Figure 1 of my drawings I have illustrated in phantom lines a reset button 39 which may be used when the thermal cut-out switch is mounted within the casing of the battery charger. This thermal reset button 39 is aligned with the extended arm portion 35 of the arm I4 so that the arm I4 may be operated manually from the outside of the battery charger.

Should a person automatically reverse the polarity of the connections of the battery charger output to the battery terminals and thereby cause an overload on the switch, the temperature responsive switch will automatically break the circuit. The bi-metal arm I2 will be heated beyond the predetermined temperature, thus breaking connection between the free end portion 24 and the latch terminal H. The operator can immediately correct the connection of the terminals to the battery. Pushing the reset button and thus urges the spring contact arm it away from the abuttable terminal I3 and into engagement with the bi-metal arm 12. Continued pushing causes the spring arm it to move the latch arm I2 and thereby resets the bi-metal arm I2 in latching engagement with the latch terminal II. The operator upon releasing the pressure on the reset button 39 and thus on the spring contact arm M will permit the spring properties on the arm to snap it into engagement with the abuttable terminal I3 thus completin the circuit.

No current can flow through the circuit and through the bi-metal arm I2 until the pressure against the spring arm I4 is released and the arm snaps back against the abuttable terminal I3. My new thermal cut-out switch thus eliminates any .possibility of welding the bi-metal latch arm I2 to the latch terminal II and also eliminates any possibility of excessive sparking therebetween which would burn the contact surface of the latch terminal and the latch arm. The operator cannot hold the bi-metal arm I2 in contact with the latch terminal I! while the circuit is overloaded and burn his fingers. My thermal cut-out switch will latch and open indefinitely under overload conditions without any damage to the delicate bi-metal temperature responsive switch.

Although the invention has been described in its preferred form with a certain degree of par- 7 ticularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. A thermal cut-out switch comprising, an insulation support member having first and second sides, a current conducting latch terminal provided with a latch edge and fastened on said second side, a current conducting bimetal latch arm fastened on said first side and having a transverse end portion thereof extendible to said second side for current conducting enlatchment over the edge of said latch terminal, a current conducting abutment terminal on said first side and spaced from said latch arm, and a current conducting spring arm fastened on said first side and electrically connected to said latch arm and manually abuttable against said bimetal latch arm and also abuttable against said abutment terminal, said spring arm having springlike properties urging the same away from said latch arm and into current conducting contact against said abutment terminal thus establishing a series electrical circuit through said arms and said terminals.

2. A thermal cut-out switch comprising, an insulation support member having first and second sides and an opening therethrough, a current conducting latch terminal provided with a latch edge and fastened on said second side and extending at least partly across said opening, a current conducting bimetal latch arm fastened on said first side and having a transverse end portion thereof extendible through said opening for current conducting enlatchment over the edge of said latch terminal, a current conducting abutment terminal on said first side and spaced from said latch arm, and a current conducting spring arm fastened on said first side and electrically connected to said latch arm and manually abuttable against said bimetal latch arm and also abuttable against said abutment terminal, said spring arm having spring-like properties urging the same away from said latch arm and into current conducting contact against said abutment terminal thus establishing a series electrical circuit through said arms and said terminals- EMIL ARTHUR HAVAS-I.

CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,812,162 Maple June 30, 1931 2,191,588 Sattler Feb. 27, 1940 

